Ammonium oxalate as an efficient catalyst for one-pot synthesis of tetrahydrobenzo [a]xanthen-11-one derivatives under solvent-free conditions

Article abstract of DOI:10.1080/15533174.2012.754767

A simple and efficient procedure for the synthesis of 12-aryl- or 12-alkyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives has been developed via one-pot three-component reaction of 2-naphthol, aldehydes, and dimedone in the presence of ammonium ox

Full text of DOI:10.1080/15533174.2012.754767

This article was downloaded by: [University of Tennessee, Knoxville]
On: 20 February 2013, At: 06:26
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt20
Ammonium oxalate as an efficient catalyst for one-
pot synthesis of tetrahydrobenzo [a]xanthen-11-one
derivatives under solvent-free conditions
Hamid R. M. Esfahani a , Naser Foroughifar a , Akbar Mobinikhaledi b & Hassan Moghanian c
a Department of Chemistry, Tehran North Branch, Islamic Azad University, Tehran, Iran
b Department of Chemistry, Faculty of Science, Arak University, Arak, 38156-8-8349, Iran
c Young Researchers Club, Dezful Branch, Islamic Azad University, Dezful, Iran
Accepted author version posted online: 19 Feb 2013.
To cite this article: Hamid R. M. Esfahani , Naser Foroughifar , Akbar Mobinikhaledi & Hassan Moghanian (2013):
Ammonium oxalate as an efficient catalyst for one-pot synthesis of tetrahydrobenzo [a]xanthen-11-one derivatives
under solvent-free conditions, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
DOI:10.1080/15533174.2012.754767
To link to this article: http://dx.doi.org/10.1080/15533174.2012.754767
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service
to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting,
typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of
the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the
content, and all legal disclaimers that apply to the journal relate to this version also.
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

ACCEPTED MANUSCRIPT
Ammonium oxalate as an efficient catalyst for one-pot synthesis of tetrahydrobenzo
[a]xanthen-11-one derivatives under solvent-free conditions
Hamid R. M. Esfahani,1 Naser Foroughifar,*1 Akbar Mobinikhaledi2 and Hassan
Moghanian3
1Department of Chemistry, Tehran North Branch, Islamic Azad University, Tehran, Iran
2Department of Chemistry, Faculty of Science, Arak University, Arak 38156-8-8349,Iran
3Young Researchers Club, Dezful Branch, Islamic Azad University, Dezful, Iran
E-mail: N_foroughifar@yahoo.com; Tel.: +98-861-4173402; Fax: +98-861-4173406;
Abstract:
A simple and efficient procedure for the synthesis of 12-aryl- or 12-alkyl-8,9,10,12-
tetrahydrobenzo[a]xanthen-11-one derivatives has been developed via one-pot three-component
reaction of 2-naphthol, aldehydes and dimedone in the presence of ammonium oxalate as a mild
and inexpensive catalyst under solvent-free conditions. The present method is operationally
simple and offers several advantages such as high yields, short reaction time, economic
availability of the catalyst and simple workup.
Keywords: Xanthene, ammonium oxalate, multi-component, one-pot, solvent-free
1
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Introduction
The synthesis of xanthenes, especially benzoxanthenes has gained considerable attention in
organic synthesis due to their wide range of biological and pharmaceutical properties such as
antibacterial [1], antiviral [2], anti-inflammatory activities [3] and sensitizers in photodynamic
therapy for destroying the tumor cells [4]. Further, these compounds have found wide usage such
as leuco-dyes, in laser technologies, and as pH-sensitive fluorescent materials for visualization of
biomolecules [5, 6].
Xanthenes and benzoxanthenes are prepared by different methods involving trapping of
benzynes by phenols [7], cyclocondensation reaction between 2-hydroxyaromatic aldehydes and
2-tetralone [8], the reaction of aldehydes with 2-naphthol [9], intramolecular phenyl carbonyl
coupling reactions of benzaldehydes and acetophenones [10] and reaction of 2-naphthol with 2-
naphthol-1-methanol [11]. Recently, the synthesis of benzoxanthenes has been achieved by the
condensation of aldehydes, 2-naphthol and cyclic 1,3-dicarbonyl compounds by
cyclodehydration in the presence of various catalysts such as NaHSO4-SiO2 [12], Sr(OTf)2 [13],
para-toluenesulfonic acid (p-TSA) [14], ceric ammonium nitrate (CAN) [15], InCl3 [16],
H3PW12O40 [17], NH4Cl [18] and sulfamic acid [19]. However, these methods show varying
degrees of success as well as limitations such as prolonged reaction times, low yields, use of
toxic solvents, requirement of excess of reagents/catalysts, laborious work-up procedures, the
requirement of special apparatus, or harsh reaction conditions. Thus, the development of milder
and clean procedures is highly demanding for the synthesis of benzoxanthenes.
2
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Results and Discussion
As a continuation of our recent studies, devoted to the development of practical, safe and
environmentally friendly procedures for some important transformations [18, 20, 21], we wish to
report an efficient, convenient and facile procedure for the condensation of aldehydes, dimedone,
and 2-naphthols to the corresponding benzoxanthenes in the presence of inexpensively available
ammonium oxalate under solvent-free conditions in good to excellent yields without any by-
products (Scheme 1).
Scheme 1.
First, to evaluate the synthetic potential of the proposed procedure and to optimize the reaction
conditions, the reaction of 3-nitrobenzaldehyde, dimedone and 2-naphthol in the presence of
ammonium oxalate was examined in different solvent and solvent-free conditions. As can be
seen from Table 1, the best result was obtained under solvent-free conditions at 110 °C. Next, to
evaluate the effect of catalyst concentration, the model reaction was carried out in the presence
of different amounts of catalyst at 110 °C. The result showed that for the model reaction 10
mol% of catalyst was sufficient to achieve a fairly high yield (Table 1). A slight excess of the
dimedone was found to be advantageous, and hence the molar ratio of 2-naphthol to dimedone
was kept as 1:1.1.
Table 1.
With the optimized conditions in hand, to explore the generality of the reaction, we extended our
study using ammonium oxalate as catalyst under solvent-free conditions with different aromatic
aldehydes bearing electron withdrawing groups and electron-releasing groups to prepare a series
3
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
of tetrahydrobenzo [a]xanthen-11-one derivatives in good to excellent yields (Table 2). On the
basis of the results listed in Table 2, this reaction is affected by electronic and steric factors.
However, with aromatic aldehydes with electron-withdrawing groups as substrates, the reaction
time is shorter than those with electrondonating groups. Ortho-substituted aromatic aldehydes
(such as 2-chlorobenzadehyde) gave lower yields because of the steric effects.
Table 2.
On the other hand, aliphatic aldehydes such as propionaldehyde and heterocyclic aldehydes such
as indol-3-carbaldehyde were also examined under the same conditions, and the corresponding
products were obtained successfully. The reactions with aliphatic and heterocyclic aldehydes
provided somewhat lower yields than those with aromatic aldehydes (Table 2), probably due to
less stability of o-quinonemethide intermediate (o-QMs).
The results obtained from the condensation reaction of benzaldehyde, 2-naphthol and dimedone
under optimized conditions were compared to the best ones published so far for this reaction
using different catalysts, the data listed in Table 3. In this study it was found that ammonium
oxalate is a more efficient and superior catalyst (Entry 1) over other catalysts with respect to
reaction time and yield of the desired xanthene.
Table 3.
Experimental
All products were characterized by a comparison of their spectral data or by comparison of their
physical and spectroscopic data with those reported in the literature. IR spectra were recorded as
KBr disc on a galaxy series FT-IR 5000 spectrometer. NMR spectra were recorded on a brucker
spectrometer (300 MHz) in CDCl3 with TMS as an internal standard.
4
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
General procedure for tetrahydrobenzo[a]xanthen-11-one derivatives
A mixture of aldehyde (1 mmol), 2-naphthol (1 mmol), dimedone (1.1 mmol), and ammonium
oxalate (0.1 mmol) was stirred magnetically at 110 °C for the appropriate time as shown in Table
2. The reaction progress was followed by TLC. When the reaction was completed, the mixture
was cooled to room temperature and a mixture of EtOH-H2O (10 mL, 1:1) was added, and the
mixture was stirred for 15 min. The obtained solid product was filtered and recrystallized from
ethanol to yield pure xanthene derivatives.
Representative Spectral Data
Table 2, Entry 6
IR (KBr): νmax = 3530, 3182, 1661, 1595, 1512, 1372, 1228, 1175, 837, 820 cm-1; 1H NMR (300
MHz, CDCl3): δ= 9.30 (s, 1H), 7.81 (d, J = 9.0 Hz, 2H), 7.71 (d, J = 8.1 Hz, 1H), 7.44-7-36 (m,
3H), 7.05 (t, J = 6.1 Hz, 2H), 6.66 (t, J = 7.5 Hz, 2H), 5.81 (s, 1H), 2.64 (s, 2H), 2.45 and 2.38
(AB system, J = 16.0 Hz, 2H), 1.18 (s, 3H), 1.02 (s, 3H); 13C NMR (75 MHz, CDCl3): δ= 201.0,
167.3, 153.3, 148.3, 133.2, 132.0, 131.6, 129.6, 129.2, 128.7, 128.3, 127.9, 125.7, 123.9, 122.0,
119.3, 117.9, 117.0, 114.4, 50.7, 42.0, 32.8, 29.5, 28.5, 27.7.
Table 2, Entry 9
IR (KBr): νmax = 3210, 3059, 2960, 1643, 1595, 1516, 1377, 1226, 1175, 1095, 815, 739 cm-1; 1H
NMR (300 MHz, CDCl3): δ= 8.03 (d, J = 8.5 Hz, 1H), 7.80 (t, J = 9.2 Hz, 2H), 7.46-7.35 (m,
3H), 7.01 (s, 1H), 6.79 (d, J = 7.3 Hz, 1H), 6.68 (d, J = 7.1 Hz, 1H), 5.71 (s, 1H), 3.84 (s, 3H),
3.78 (s, 3H), 2.59 (s, 2H), 2.35 and 2.29 (AB system, J = 15.4 Hz, 2H), 1.15 (s, 3H), 1.01 (s,
5
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
3H); 13C NMR (75 MHz, CDCl3): δ= 197.4, 164.2, 149.0, 148.2, 147.7, 138.0, 131.9, 129.2,
128.8, 127.4, 125.3, 124.1, 120.9, 118.2, 117.4, 114.8, 112.4, 111.3, 56.3, 56.1, 41.9, 34.5, 32.7,
29.8, 27.5.
Table 2, Entry 10
IR (KBr): νmax = 3007, 2953, 1653, 1591, 1502, 1375, 1323, 1222, 1122, 1008, 817, 760 cm-1; 1H
NMR (300 MHz, CDCl3): δ= 8.04 (d, J = 8.6 Hz, 1H), 7.81 (t, J = 8.9 Hz, 2H), 7.51-730 (m,
3H), 6.58 (s, 2H), 5.70 (s, 1H), 3.77 (s, 6H), 3.76 (s, 3H), 2.60 (s, 2H), 2.33 (s, 2H), 1.15 (s, 3H),
13
1.04 (s, 3H); C NMR (75 MHz, CDCl3): δ= 197.4, 164.4, 153.3, 148.2, 140.9, 136.8, 131.9,
129.3, 128.8, 124.4, 125.4, 124.1, 118.0, 117.4, 114.7, 106.2, 61.1, 56.5, 51.3, 41.9, 35.1, 32.7,
29.7, 27.6.
Table 2, Entry 13
1
IR (KBr): νmax = 3045, 2973, 1649, 1593, 1512, 1372, 1229, 1132, 814 cm-1; H NMR (300
MHz, CDCl3): δ= 8.08 (d, J = 8.8 Hz, 1H), 7.79 (t, J = 8.6 Hz, 2H), 7.48-7.21 (m, 5H), 6.58 (d, J
= 9.1 Hz, 2H), 5.66 (s, 1H), 2.86 (s, 6H), 2.60 (s, 2H), 2.34 and 2.28 (AB system, J = 14.7 Hz,
2H), 1.15 (s, 3H), 1.03 (s, 3H); 13C NMR (75 MHz, CDCl3): δ= 197.4, 163.8, 149.3, 148.1,
133.7, 132.0, 129.4, 128.9, 128.7, 127.3, 125.2, 124.3, 118.8, 117.5, 115.1, 112.8, 51.4, 41.9,
41.0, 43.0, 32.7, 29.7, 27.9.
Table 2, Entry 14
1
IR (KBr): νmax = 3047, 2980, 2935, 1653, 1597, 1518, 1373, 1222, 1170, 1018, 797 cm-1; H
NMR (300 MHz, CDCl3): δ= 8.25 (d, J = 8.5 Hz, 1H), 7.83 (d, J = 8.4 Hz, 1H), 7.78 (d, J = 8.6
Hz, 1H), 7.55 (t, J = 9.2 Hz, 1H), 7.46 (t, J = 9.0 Hz, 1H), 7.30 (t, J = 8.9 Hz, 1H), 5.96 (d, J=
1.8 Hz, 1H), 5.82 (s, 1H), 5.76 (d, J= 1.6 Hz, 1H), 2.63 (s, 2H), 2.39 (s, 2H), 2.13 (s, 3H),), 1.19
6
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
13
(s, 3H), 1.16 (s, 3H); C NMR (75 MHz, CDCl3): δ= 197.1, 165.6, 154.6, 151.0, 148.2, 132.0,
131.8, 129.2, 128.8, 127.3, 125.4, 124.0, 117.6, 116.1, 111.6, 107.2, 106.6, 51.3, 41.9, 32.7, 29.9,
28.7, 27.5.
Table 2, Entry 15
1
IR (KBr): νmax = 3055, 2953, 2928, 1647, 1593, 1514, 1377, 1223, 1143, 1028, 810 cm-1; H
NMR (300 MHz, CDCl3): δ= 8.16 (d, J = 8.3 Hz, 1H), 7.77 (d, J = 6.0 Hz, 2H), 7.58 (d, J = 8.5
Hz, 1H), 7.40-7.23 (m, 5H), 7.20 (s, 1H), 7.07 (s, 1H), 6.06 (s, 1H), 2.66 and 2.60 (AB system, J
= 16.7 Hz, 2H), 2.33 and 2.24 (AB system, J = 18.8 Hz, 2H) 1.14 (s, 3H), 0.94 (s, 3H); 13C NMR
(75 MHz, CDCl3): δ= 197.9, 164.3, 147.9, 136.8, 132.2, 131.9, 129.0, 128.7, 127.1, 125.1, 124.1,
123.9, 121.9, 119.8, 119.6, 119.7, 117.8, 117.4, 113.8, 111.6, 100.4, 51.4, 41.8, 32.7, 29.5, 27.9,
27.0
Conclusion
In conclusion, we have developed a simple and efficient methodology for the synthesis of
tetrahydrobenzo[a]xanthene-11-one derivatives in the presence of ammonium oxalate under
solvent-free conditions. The advantages of this method over other existing methods are reduced
reaction times, higher yields, mild reaction condition, easy purification and economic viability of
the catalyst.
Acknowledgment
7
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
We gratefully acknowledge the financial support from the Research Council of Islamic Azad
University, Tehran North Branch.
References
[1] El-Brashy, A. M.; Metwally, M. E.; El-Sepai, F. A. Spectrophotometric determination of
some fluoroquinolone antibacterials by binary complex formation with xanthene dyes. II
Farmaco 2004, 59, 809-817.
[2] Jamison, J. M.; Krabill, K.; Hatwalkar, A. Potentiation of the antiviral activity of poly r(A-U)
by xanthene dyes. Cell Biology International Reports 1990, 14, 1075-1084.
[3] Chibale, K.; Visser, M.; Schalkwyk. D. V.; Smith, P. J.; Saravanamuthu, A.; Fairlamb, A. H.
Exploring the potential of xanthene derivatives as trypanothione reductase inhibitors and
chloroquine potentiating agents. Tetrahedron 2003, 59, 2289-2296.
[4] Ion, R. M.; Frackowiak, D.; Wiktorowicz, K. The incorporation of various porphyrins into
blood cells measured via flow cytometry, absorption and emission spectroscopy. Acta
Biochimica Polonica 1998, 45, 833-845.
[5] Bhowmik, B. B.; Ganguly, P. Photophysics of xanthene dyes in surfactant solution.
Spectrochim. Acta, Part A 2005, 61, 1997-2003.
[6] Foroughifar, N.; Mobinikhaledi, A.; Moghanian, H. A Catalytic and Green Procedure for
Synthesis of 12-Aryl or 12-Alkyl-8,9,10,12-Tetrahydrobenzo[a]xanthen-11-one derivatives
under Solvent-Free Conditions. International Journal of Green Nanotechnology: Physics and
Chemistry 2009, 1, 57-63.
[7] Knight, D. W.; Little, P. B. The first high-yielding benzyne cyclisation using a phenolic
8
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
nucleophile: A new route to xanthenes. Synlett 1998, 1141–1143.
[8] Jha, A.; Beal, J. Convenient synthesis of 12H-benzo[a]xanthenes from 2-tetralone.
Tetrahedron Lett. 2004, 45, 8999-9001.
[9] Van Allan, J. A.; Giannini, D. D.; Whitesides, T. H. Dibenzoxanthene derivatives and related
products from b-naphthol and aldehydes or acetals. J. Org. Chem. 1982, 47, 820-823.
[10] Kuo, C. W.; Fang, J. M. Synthesis of xanthenes, indanes, and tetrahydronaphthalenes via
intramolecular phenyl–carbonyl coupling reactions. Synth. Commun. 2001, 31, 877-892.
[11] Sen, R. N.; Sarkar, N. The condensation of primary alcohols with re- sorcinol and other
hydroxy aromatic compounds. J. Am. Chem. Soc. 1925, 47, 1079-1091.
[12] Das, D.; Laxminarayana, K.; Krishnaiah, M.; Srinivas, Y. An efficient and convenient
protocol for the synthesis of novel 12-aryl- or 12-alkyl-8,9,10,12-tetrahydrobenzo[a]-xanthen-
11-one derivatives. Synlett 2007, 3107-3112.
[13] Li, J.; Tang, W.; Lu, L.; Su, W. Strontium triflate-catalyzed one-pot condensation of 2-
naphthol, aldehydes, and cyclic 1,3-dicarbonyl compounds. Tetrahedron Lett. 2008, 49, 7117-
7120.
[14] Khurana, J. M.; Magoo, D. p-TSA-catalyzed one-pot synthesis of 12-aryl-8,9,10,12-
tetrahydrobenzo[a]xanthen-11-ones in ionic liquid and neat conditions. Tetrahedron Lett. 2009,
50, 4777-4780.
[15] Kumar, A.; Sharma, S.; Maurya, R. A.; Sarkar, J. Diversity-oriented synthesis of
benzoxanthene and benzochromene libraries via one-pot, three-component reactions and their
anti-proliferative activity. J. Comb. Chem. 2010, 12, 20-24.
9
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
[16] Nandi, G. C.; Samai, S.; Kumar, R.; Singh, M. S. An efficient one-pot synthesis of
tetrahydrobenzo[a]xanthene-11-one and diazabenzo[a]anthracene-9,11-dione derivatives under
solvent-free condition. Tetrahedron 2009, 65, 7129-7134.
[17] Wang, H.-J.; Ren, X.-Q.; Zhang, Y.-Y.; Zhang, Z.-H. Synthesis 12-aryl or 12-alkyl-8,
9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives catalyzed by dodecatungstophosphoric
acid. J. Braz. Chem. Soc. 2009, 20, 1939-1943.
[18] Foroughifar, N.; Mobinikhaledi, A.; Moghanian, H.; Mozafari, R.; Esfahani, H. R. M.
Ammonium chloride catalyzed one-pot synthesis of tetrahydrobenzo [α]xanthen-11-one
derivatives under solvent-free conditions. Synth. Commun. 2011, 41, 2663-2673.
[19] Heravi, M. M.; Alinejad, H.; Bakhtiari, K.; Oskooie, H. A. Sulfamic acid–catalyzed solvent-
free synthesis of 10-aryl-7,7-dimethyl-6,7,8,10-tetrahydro-9H-[1,3]-dioxolo[4,5-b]- xanthen-9-
ones and 12-aryl-9,9-dimethyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-ones. Mol. Divers.
2010, 14, 621-626.
[20] Foroughifar, N., Mobinikhaledi, A., Moghanian, H. Simple and efficient method for
synthesis of novel 4-substituted 1-acylthiosemicarbazides via one-pot multicomponent reactions.
Synth. Commun. 2009, 39, 3668-3676.
[21] Foroughifar, N., Mobinikhaledi, A., Moghanian, H. A straightforward and efficient catalyst-
free one-pot synthesis of N-Acyl-1,3-diaryl-2-azaphenalene derivatives via multicomponent
reactions. Chem. Lett. 2010, 39, 180-181.
Table 1. Optimization of reaction conditions
10
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Solvent
Catalyst
(mol%)
Conditions
Time (min) Yield
(%)a
Entry
1
2
3
4
5
6
7
8
9
n-hexane
CH2Cl2
THF
EtOH
CH3CN
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
10
10
10
10
10
10
10
10
Reflux
Reflux
Reflux
Reflux
Reflux
RT
150
150
150
150
150
150
90
15
30
15
41
55
63
60
35
0
67
85
71
85
80 °C
110 °C
110 °C
110 °C
5
20
10
a Isolated yields
Table 2. Synthesis of tetrahydrobenzo[a]xanthene-11-one derivatives
Mp (°C)
Entry
R
Time/min
Yield/%a
Found
149-150
180-181
Reported lit.
1
2
3
4
5
6
7
8
9
C6H5
2-ClC6H4
18
20
15
15
12
25
20
20
20
88
70
90
85
91
66
74
75
70
151-153 [19]
179-180 [19]
180-182 [19]
168-170 [19]
180-181 [19]
-
240-241 [19]
204-205 [19]
-
4-ClC6H4
187-188
170-171
173-174
226-227
241-242
206-207
157-158
3-NO2C6H4
4-NO2C6H4
2-OHC6H4
3-OHC6H4
4-MeOC6H4
3,4-diMeOC6H3
3,4,5-
triMeOC6H2
4-Me C6H4
4-FC6H4
10
20
76
197-198
-
11
12
13
14
15
12
20
30
78
80
85
50
191-193
183-185
196-197
175-176
196-198 [19]
185-186 [20]
4-N(Me)2C6H4
5-Mefurfural
-
-
Indol-3-
carbaldehyde
15
30
25
45
58
141-143
Liquid
-
16
Propanal
a Isolated yields
Liquid [16, 18 ]
11
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table 3. Comparison of different catalysts for reaction of benzaldehyde, dimedone and 2-
naphthol
Conditions
Yield/
%
Entry Catalyst
Time/min
a
Solvent-free /110
ºC
ClCH2CH2Cl / 60
ºC
Solvent-free /120
ºC
Solvent-free /120
ºC
Solvent-free /120
ºC
Solvent-free /120
ºC
Solvent-free / 60
ºC
1
2
3
4
5
6
7
(NH4)2C2O4
18
300
45
30
30
15
70
88
Sr(OTf)2
p-TSA
CAN
85 [16]
88[ 17]
94 [18]
84 [19]
86 [21]
86 [20]
InCl3
NH4Cl
H3PW12O40
a Isolated yields.
O
O
R
O
OH
(NH4)2C2O4
+
RCHO
+
Solvent-free,
110 oC
O
Scheme 1. Synthetic pathway for synthesis of tetrahydrobenzo [α]xanthen-11-one derivatives
12
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
13
ACCEPTED MANUSCRIPT